1. Technical Field
The present invention relates to holographic memories, holographic storage systems and holographic processors.
2. Background Art
The traditional advantages of 3-D holographic memories are high storage density and parallel access capability. These features were recognized in the early 1960's and serious efforts towards the practical implementation of such memories were undertaken. Unfortunately, these efforts did not produce commercially viable memories. In recent years there has been a resurgence of interest in 3-D optical storage due to a considerable improvement in the understanding and availability of storage media, a dramatic improvement in opto-electronic components in general, and most importantly, the emergence of applications, such as image processing, neutral networks, and data bases where the capabilities of these memories can be effectively utilized. This recent activity has culminated in the storage of 10.sup.4, 320.times.220-pixel holograms in a volume roughly equal to 2 cm.sup.3. If spatial light modulators with 1 million pixels are used, then the storage density achievable today is in excess of 10.sup.9 bits per cm.sup.3.
Volume holograms are usually recorded using angular, wavelength, phase code, and spatial multiplexing. In addition, peristrophic multiplexing, a holographic technique that applies to either thin or thick (3-D) media, was recently introduced. Any of these methods, or certain combinations of them, can be used to multiplex holograms for holographic storage devices. All of these methods employ a reference beam consisting of a single plane wave, which may have a phase code imprinted on the wavefront.
It is an object of the present invention to exploit the use of non-plane waves in the reference beam to implement multiplexing. It is a further object of the invention to perform multiplexing without requiring anything more than a relative translation between the holographic recording media and optical (signal and reference) beams.